Automatic telephone system



June 24, 1941. w. SCHWENN AUTOMATIC TELEPHONE- SYSTEM Filed Dec. 21,1938 2 Sheets-Sheet 1 (N bi- INVENTOR. WILL! SCHWENN June 24, 1941. w.SCHWENN AUTOMATIC TELEPHONE SYSTEM 2 Sheets-Sheet 2 Filed Dec. Zl, 1938WILL! SCHWENN W M ATTORNEY.

Patented June 24, 1941 2,247,254 AUTOMATIC TELEPHONE SYSTEM WilliSchwenn, Berlin-Charlottenburg, Germany,

assignor to Fides Gesellschaft fur die Verwaltung und Vcrwertung vongewerblichen Schutzrechten mit beschrankter Haftung, Berlin, Germany, acorporation of Germany Application December 21, 1938, Serial No. 246,988

In Germany December 24, 1937 12 Claims. (01. 179-23) The inventionrelates to automatic telephone installations in which a local, forexample, a sub-exchange is supplied with current from the lighting mainsin which on failure of the power supply, receives current over ajunction line from the main exchange.

With known arrangements of this kind the case is simple as underundisturbed condition of the installation the dialled impulses do not.

main exchange on failure of the power supply is very much more difficultwhen dealing with installations in which both-way operation is effectedand the dialling pulses are transmitted as inductive direct currents oralternating currents. In such installations on account of the necessityof good impulsing and speech transmission, contrary to the knownarrangements, no current feeding source can be applied to the connectingline under normal circumstances. In order in such systems, to ensure theauxiliary feeding means to the sub-exchange from the main exchange thereare, in accordance with the invention, at the ends of the connectingline supervisory means provided which on failure of the local currentsupply bring into operation. switching means at the sub-exchange andthese effect the connection of a source of current in the main exchangeHVSt to the junction lines.

The invention will best be understood by reference to the specificationand the accompanying drawings, in which Fig. 1 is a schematicdiagramil-lustrating a sub-exchange UVST, a main exchange -I-IVSt,interconnecting trunk line FL, and the associated switching apparatus ineach exchange. Figs 2A and 2B show the detail circuits of the schematicdiagram which are necessary for a complete understanding of theinvention. Fig. 2A shows the equipment in the sub-exchange at one :endof the trunk line FL and Fig. 2B shows the equipment in the mainexchange at the other end of the trunk line FL.

Fig. 1 is aschematicdiagramof the arrangement by which the sub-exchangeUVSt is con.- nected through transformers Trl, TrZ inthe two-way trunkline FL to the main exchange.

scriber, Tl for example, on taking down his rer The subscriber cf thesub-exchange is fed with ceiver causes a callfinder AS to set itself onthe calling line. By means of his calling dial the subscriber sends outimpulses which position the line selector connected to the call finderon :to the terminals of the desired subscriber, say, T2.

Connections which pass from the sub-exchange over the line FL to themain exchange can be effected in two Ways. Either the subscriber, aftera call finder has set itself on his line selects, by dialling a specialdigit, the line .selectorLW which is connected via repeater Uel to lineL3. Further digits are then transmitted from the repeater Uel via thetransformer TrLline .FL to the transformer Tr2, repeater Ue2, groupselector GW3 of the main exchange. The direct current pulses from thecalling subscriber become inductive direct current pulses in therepeater Uel. These impulses pass as such over the lineFL and inrepeater Ue2 at the main exchange are transformed again into pure directcurrent pulses. There is the further possibility of asubscriber of thesub-exchange UVSt to effect connections to the main exchange via thecall finder and line selector if, after taking down his receiver, hepresses a key and thereby causes the operation of a mixing selector MWat the sub-exchange which sets itself on his line. When the selector MWhas found the calling line, the call finder AS is released and returnsto its home position. The dialling pulses from the calling subscriber Tlpass over the line TL, resting contact w, line Ll, mixing selector MW,repeater Uel, transformer Trl, resting contact v, line FL, restingcontact 1/, transformer Tr2, contact a to the group select0rGW3.

Connections from the main to the sub-exchange pass from the groupselector GWI over resting contact a of the change-over switchingarrangement Ub, resting contact a of the re-' peater U62, transformerTr2, resting contact y of the change-over switching arrangement Uh, lineFL, resting contact 1;, transformer Trl, repeater Uel, mixing selectorMW to the call finder AS. The call finder starts up and sets itself onthe calling line La which is, similarly to a subscribers line, connectedto the contact bank of the call finder. The direct current pulses fromthe group selector GWI of the main exchange are transformed intoinductive direct current pulses in the repeater UeZ and are transmittedover the line FL to the repeater Uel of the sub-exchange. In therepeater Uel, the inductive pulses are transformedback into pure directcurrent pulses and pass as such to the line selector LW. The lineselector is then set on the terminals of the called subscriber. Amongthe subscribers of the sub-exchange is one, TI according to the examplegiven, privileged in so far as by failure of the power supply he isconnected to the contacts to and c of the change-over switchingarrangement so that line TL is immediately connected via line L2 to theline FL and switched through to the main exchange. At the main exchangeon the failure of the power supply at the sub-exchange, contacts y and11, of the switching arrangement Ub reverse. Subscriber Tl can set upoutgoing calls which, at the main exchange, pass via the preselector VWand the group selector GWZ. He can also receive calls from the mainexchange which pass via group selector GW I, the reversed contact a ofUb, the repeater Ue3, the home contact of the preselector VW, thereversed contact of U1), the line FL, reversed contact '0 of Ua, lineL2, reversed contact to the subscribers line TL. If in the directionmain to sub-exchange a call does not, as in Fig. 1 arrive over a groupselector GWI, but comes via a line selector, then repeater Ue 3 in themain exchange can be dispensed with as calling current can be sent outfrom the line selector to the privileged subscriber.

In Figs. 2A and 2B the circuit details of the schematic are shown so faras these are necessary to an understanding of the invention.

The current feeding arrangements of the subexchange UVSt are effected inknown manner through a rectifier connected to the alternating supply WQ.7 I

Current from the supply'WQ through the rectifier is'fed" to thesupervisory relays W and V over the circuit: 60 volts, windings ofrelays W and V, contact 'Ia', earth. So long as current is deliveredfrom WQ, both relaysW and V are energized. Parallel to the relay W is acondenser Cp of large capacity so that relay-W requires a greateroperating time than relay V. The purpose of this arrangement isexplained later. When relays W and V are energized, the subscribersstation TI is connected to the wires al/bl which correspond to the lineL! of Fig. 1 via contacts 2'10 and 4w. The junction line FL isconnectedto the transformer TTI at the subexchange, the upper wire ofvia contacts H12 and-l 13wv and the lower wire bf via contact 61).Repeater Uel is reached by the transformer Trl The setting up ofconnections under normal conditions is not pertinent to the inventionand will therefore not be described.

If the current supplyat the sub-exchange fails, the supervisory relays Wand V of the changeover switching arrangement Ua release. Station TI isnow switched directly on to the line FL. As aresult of this operation atthe sub-exchange the current feeding source at the main exchange isconnected to the line FL. After the switching over the followingcircuitis formed for the relay S of the change-over group Ub at the mainexchange earth, indicator SZ at station Ti, choke coil Dral, contact Ir,I31) of change-over group ca, wire of of line FL, upperhalf winding oftransformer Tr2, contact 3071, winding I of relay S, contact 32y,winding II of relay S, battery, earth. Relay S of the change-over groupUb operates in this circuit and closes the following circuit for relayY: earth, contact Ms, winding of the slowacting relay Y, battery, earth.

Relay-Y closes the following circuit for relay U: earth, contacts 36y,35s, winding of relay U,

battery, earth. Relay Y at contact lBy inter-- rupts the connecting ofline FL to transformer Tr2 while simultaneously at contact l9y thefeeding bridge relay A is connected to the lower wire of the line FL.Relay S is connected to the upper wire line FL via contact Hu and, afterrelay Y has operated, the high resistance winding of relay S isdisconnected by the opening of contact 32y. Relay S locks up over:earth, battery, Wi of low resistance, contact Ely, winding I of relay S,contact 39h, Ilu, wire a) of the line FL, contacts i311, 1x, choke coilDral, indicator SZ, earth. At contact lliu the circuit for connectingline FL to the preselector VW is prepared. Relay U prepares further byclosure of its contacts Mu, the busy circuit for incoming calls.

When the subscriber Ti of the sub-exchange takes down his receiver toefiect a connection the following circuit is closed; earth, winding ofrelay A in the main exchange, contact 193/, wire bf, contact 522,winding III of the relay X in the subexchange, contact 320, closedsubscribers loop Tl, contact lw, windings I and II of relay X, contactI322, wire of, contacts Wu, 3071., winding I of relay S, contact My,resistance W2, battery, earth. 7

Relay X at the sub-exchange operates in this circuit and relay A at themain exchange. Relay X by means of its contacts 1x and 9x disconnectsboth choke coils Dral and DTaZ and at the same time the circuit of theindicator SZ and the earth potential. Further, relay X at its contact 8rshort-circuits its own winding II so that it operates as aslow-to-release relay during the loop interruptions resulting fromdialling.

In the change-over group Ub at the main exchange, relay A by means ofits contact 2111 closes the following loop to the calling relay Row ofthe preselector VW: earth, battery, winding I of relay Row, contact 15of the test relay of the selector, contact 28drb, winding II of relayDrb, contact 21a, contact if, winding II of relay Row, earth. Thecalling relay operates in this circuit and effects in known manner" thestart of the preselector VW. As soon as the preselector has left itshome position, relay E, previously energized by direct current, of therepeater Ue3, releases. This has the result that U63 can no longer beseized via group selector GWI in the incoming direction; Relay Afurther, at its contact 28a, switches through the wire a to thepre-selector VW. The opening of contact 2 la disconnects the callingrelay R from the talking wires. When the preselector VW has found a freegroup selector, the test relay T operates.

Subscriber Tl receives in known manner dialling tone from the groupselector seized by the preselector VW over the following circuit: a wirefrom the group selector, a wiper of the preselector VW, contacts t,261;, 29a, talking condenser, contact l6u, wire of, contact I31), c,condenser C2, contact lw, subscriber station Tl, contact 3w, condenserC3, contact 50, wire bf, contact 19y, talking condenser, contact 24q,contacts t, b wiper of preselector, b wire of group selector.

If the subscriber now dials to set the group 7 and line selectors, hisloop circuit is alternately opened and closed. Thereby relays A and S ofthe change-over group Ub are impulsively released. Relay A at itscontact 21a interrupts the impulse loop to the group selector. At thefirst rel-ease of relay S a short-circuit for relay Q is opened atcontact 358. Relay Q operates in series with relay U. Relay Q bridges,at its contact 25!; the relay Drb serving as bridging choke fortheduration of theimpulse groups. The talking wires to subscriber Tl arecut off :by opening of contacts 24d and 26q during the dialling period.At the end of this, relays A and S operate continuously again. Resultingfrom this relay Q releases. The talking wires to the calling su'bscriberare again switched through. Further, relay Drb again operates and atitscontact 28 drb interrupts the short-circuit on its highlyinductive'winding I. Further processes for effecting the connection arenot part of the inventionand are therefore not described. At the end ofthe conversation when subscriber Tl hangs up the receiver, relay X inthe sub and relay A in the main exchange release which brings about therelease of the preselector and the selector seized by it. Relay S at themain exchange is held energized over the earth potential and theindicator S2 at subscriber station Tl in the following circuit: earth,indicator SZ, choke coil Dml, contact 1r, I31), wire of, contacts flu,30h, winding I of relay S, contact 3| resistance Wi, battery, earth.Relay S maintains relays Y and U energized. In this way the feedingbattery in the main exchange remains connected to the line FL. Ifsubscriber Tl of the sub-exchange is, after failure of the power supply,desired for a connection from the main exchange via the group selectorGWI, relayA-3 in the calling repeater U63 operates via: earth, battery,wiper c of group selector GWI, contacts Mu, 50c, 5M3, 5303, 54112, 55q3,winding III of relay A3, earth. Relay A3 operates and breaks at itscontact 5Ia3 the shortcircuit of the busy relayC3. C3 operates in serieswith A3 and breaks at the contact 5303 the original busy circuit. Thecircuit for winding III of relay A3 is thereby broken. Relay A3 locks upover both its windings connected to the talking wires and the loop tothe group selector: earth, winding I of relay A3, contact 3910, wiper bof the group selector 'G-W'l, loop .at group selector, wiper a of GWI,contact 382;, winding II of relay A3, battery, earth. The occupancycircuit is held via: earth, resistance W13, contact 5203, winding ofrelay C3 contacts 50c, Mu, wiper c of GWI, battery, earth. Relay C3feeds the following circuit for the relay Q3: earth contacts 1903,1833,, 11113, 15122, 14:13, winding of slow relay Q3, resistance Wifi,battery, earth. Relay Q3 at its contact 55113 disconnects the highresistance winding II of relay E from .the direct current supply whichflows via wiper c of the preselector in .its home position. Relay E isheld energized via the low resistance winding I, in the followingcircuit: earth, contacts 1.903, 8803, '66q3, winding I of relay E, wiperc of the preselector VW in the home position, test relay T of thepreselector, wiper d of VW in the home position, battery, earth.Further, relay Q3 switches through at its contacts 58q3 and 59q3, thetalking wires from the group selectorv line wipers to thechangeovergroup Ub.

If the calling subscriber now dials, a repetition of the impulses andtransmission of ringing current to subscriber TI is prevented in thefollowing manner: By the loop interruptions in the group selector GW!resulting from dialling, relay A3 of the repeater Ue3 releasesimpulsively. On the first release of .relay A3 the short circuit ofrelay V! is broken by the opening of the contact "a3. Relay VI operatesin series with relay Q3, it opens its contact Biol and thereby preventsthe application of ringing current generator *RQ. Further, it closes thefollowing circuit for relay V2: earth, contact Hui, winding II of relayV2, resistance Wid, battery, earth. During :impulse transmission relayV2 is impulsively short-circuited .at contact 10123 and locks up duringthe series of impulses. At the conclusionof the impulses relay A3operates and remains operated; Relay V2 releases due to the continuedclosing of contact Illa-3, and completes the short circuit around relayVI via contacts 74:13 and 1502; relay Vl releases. Relay V2 becomesenergized via its winding I and the 10 second switch over the followingcircuit: earth, 10 second switch, contacts 69113, 6803, 67.93, winding Iof relay V2, battery, earth. Calling current is now sent to the callreceiving relay R of the change-over group Ub over the followingcircuit: calling current generator RQ in repeater U63, contacts 6121i,

6202, winding II of relay Y3, contacts 58q3, 281 call receiving relay R,contacts 21a, 23q,24q, 5'9q3, 64s3, earth. Relay Y3 as a result of theshortcircuiting of its winding I at contact $3 is not operated by thecalling current. 0n the contrary call responding relay R operates in thechange-over group III). Via contact 331', relay H is energized. Relay 'Hat contact 22h switches the upper talking wire through to the subscriberTI. After this wire has been switched through ringing current flowsparallel to the ringing responding relay R to the subscriber Tl over thefollowing circuit: ringing generator RQ in repeater Ue3, contacts Blvl,62112, winding II "of relay Y3, contacts 58q3, 2 61], 22h, condenser"F511, wire a), contacts 132), winding II of relay 'X, condenser C2,contact lw, subscriber T-ls be'll, contacts 310, condenser C3, contact51), wire bf, contact I9y, condenser, contacts 24g, 59q3, -64s3, earth.Relay H in the change-over group "Ub cuts off the relay S from the upperwire of the line FL at contact 30h during the calling period. Relay Sduring this time is held energized in the following circuit: earth,contact 29h, winding I of relay S, contact 3ly, resistance W2, battery,earth. During the non-ringing intervals relays A and S of Ub areenergized. Relay A at its contact 21a closes the direct current loop-forrelay Y3 of the repeater Ue3. RelayY3 operates and at its contact 691 3interrupts the circuit for the call connecting relay V2. In this way thetransmission of ringing current is stopped. By the energization of relayY3, the short-circuit for relay S3 is broken at contact "U3. Relay S3operates in series with relay Q3. The connection is now established. Therelease of the connection can be effected by the called subscriber T! byback release, or by the calling subscriber. "If the called subscriber Tlhangs up, relay A in the change-over group Ub releases. Release of relayA results in the release of relay Y3 in the repeater Ue3 whereby therelease of the selectors is effected.

If the calling subscriber hangs up, the loop in the group selector GWIis broken and relay A3 in the rep-eater Ueil releases. Relay C3 is shortcircuited at contact 5M3. Relay C releases and by opening its contacts1903 and 8003, opens the holding circuit of the relays Q3 and S3. RelayQ3 is slow to release and breaks the circuit to the selector GWI at thecontact 5$q3 whereby the release of the selectors is effected.

The talking circuit to the called subscriber is broken at contacts 58q3,59113 after relay Q3 has released.

If now the called subscriber Tl hangs :up, relay A of Ub releases. Relay*8 is, however, held energized until the power network at thesubexchange is again effective.

If the power supply at the sub-exchange is restored during aconversation originating with subscriber Ti the energization of thesupervisory relays W and V during a connection over the line FL and therelay X in the feeding bridge of the main exchange, is prevented. Thelatter relay at its contact Mr breaks the circuit for both relays. At,the end of the conversation the relay X releases. Relays W and V can nowoperate. In order to prevent permanent energization of both feedingbridge relays A and S in the changeover group Ub via the repeatingwinding of the transformer Tr'l of the sub-exchange, the two supervisoryrelays W and V have differing operating times. Relay V operates firstopening its contacts 517 and I322 and closing to and Ho. Somewhat latercontact lilw closes. The loop to the main exchange is therebyinterrupted for a period of time so that relay S and the relays in thechange-over group Ub' which are dependent on this can definitelyrelease. If relay W is operated, the line FL is switched through to thetransformer Trl of the sub-exchange. In the main exchange after releaseof relay S, relays Y and U release which results in again connecting theline FL to the transformer Tr2.

What is claimed is:

1. In an automatic telephone system, a subexchange having a local sourceof operating current, a, main exchange, a trunk line interconnectingsaid exchanges, a sub-exchange subscribers station, switching equipmentin said sub-exchange controllable from said station forextending'cormections via said trunk line to said main exchange andcontrollable from said main exchangevia said trunk, line for extendingconnections to said station, means operated responsive to the failure ofsaid local operating current for disconnecting said switching equipmentand for connecting said station to said trunk line, and means in saidmain exchange operated responsive to said connection for feedingoperating current over said trunk line to permit connections to beestablished between said station and said main exchange in eitherdirection over said trunk line. 1 2. In an automatic telephone system, amain exchange, a sub-exchange, a trunk line interconnecting saidexchanges, a source of operating current for each of said exchanges, asub-exchange subscribens station, switching apparatus controllable fromsaid station for extending connections to other local stations or viasaid trunk line to said main exchange, and changeover means operatedresponsive to the failure of sub-exchange operating current fordisconnecting said apparatus and for connecting said station to saidmain exchange operating current via said trunk to thereby permit saidstation to extenddirect connections to said main exchange viasaid trunkline.

3. In an automatic telephone system, a main exchange, a sub-exchange, atrunk line interconnecting said exchanges, a source of operating currentfor each of said exchanges, a sub-exchange sulbscrib'ers station,switching apparatus controllable from said station for extendingconnections to other local stations or via said trunk line to said mainexchange, change-over means operated responsive to the failure ofsub-exchange operating current for disconnecting said apparatus and forconnecting said station to said main exchange operating current via saidtrunk to thereby permit said station to extend direct connections tosaid main exchange via said trunk line, and means in said sub-exchangeoperated responsive to the establishment of a direct connection forpreventing the reoperation of said change-over means togreconnect saidswitching apparatus. I

4. In an automatic telephone system, a main exchange, a trunk lineinterconnecting said exchanges; a source of operating current for eachof said exchanges, a sub-exchange subscribers station, switchingapparatus controllable fromrsaid station for extending connections toother local stations or via said trunk line to said main exchange,change-over means operated responsive to the failure of sub-exchangeoperating current for disconnecting said apparatus and for connectingsaid station to said main exchange op-' erating current via said trunkto thereby permit said station to extend direct connections to said mainexchange via saidtrunk line, and means in said sub-exchange operatedresponsive to the establishment of a direct connection for'preventingthe reoperation of said change-over means to reconnect said switchingapparatus in. the event that the sub-exchange operating current isreestablished. a

5. In atelephone system, a sub-exchangaa main exchange, a trunklineinterconnecting said exchanges, a local source-of operating current forsaid sub-exchange, a subscribers station, switching means in saidsub-exchange operated responsive tofailure of said operating current forconnecting said station to said trunk line, a source of operatingcurrent for said main exchange, and supervisory means in said main.exchange operated responsive to said connection for connecting said mainexchange operating current to said station via said trunk line.

6. In a telephone system, a sub-exchange, a main exchange, a trunk lineinterconnecting said exchanges, a local source of operating current forsaid sub-exchange, a subscribers station, switching means in saidsubeexchange operated responsive to failure of said operating currentfor connecting said station to said trunk line, a source of operatingcurrent for said main exchange, supervisory means in said main exchangeoperated responsive to said connection for connecting said main exchangeoperating current to said station via said trunk line, said switchingmeans in the sub-exchange controlled responsive to the reestablishmentof the localsub-exchange operating current for disconnecting saidstation from said trunk line and for restoring the supervisory means insaid main exchange to normal.

7. In a telephone system, a first exchange, a second exchange, atransformer, a trunk line interconnecting said exchanges and terminatingin said transformer at said second exchange, a local source of operatingcurrent for said first exchange, a subscribers station, switching meansin said first exchange operated responsive to the failure of saidoperating current for connecting said station to said trunk line and forplacing a potential on one conductor of said trunk line, a local sourceof operating current for said second exchange, supervisory meansconnected to the mid-point of said transformer operated over the saidone conductor of said trunk line for connecting said second exchangeoperating current to said station via said trunk line.

8. In a telephone system, a branch exchange, a main exchange, atransformer at said main exchange, a trunk line interconnecting saidexchanges and terminating at one end in said transformer, a local sourceof operating current for said branch exchange, a subscriber's station,

} switching means in said branch exchange operated responsive to thefailure of said operating current for connecting said station to saidtrunk line, supervisory means connected to the midpoint of saidtransformer operated responsive to the connection of said station tosaid trunk line, control means, auxiliary means operated responsive tothe operation of said supervisory means for connecting said supervisorymeans to said trunk line independently of said transformer and forconnecting said control means to said trunk line, and means operatedresponsive to the initiation of a call from said station for operatingsaid control means to thereby permit the extension of a connection oversaid trunk line to a subscriber in said main office.

9. A system as claimed in claim 8 including a finder switch, the controlmeans starting said finder switch to find an idle line extending to mainexchange switching apparatus and repeating dialled impulses receivedfrom the said station to thereby control said switching apparatus toextend the connection to a main exchange subscriber.

10. In a telephone system, a main and a subexchange, a trunk linebetween said exchanges, subscribers lines terminating in said exchanges,automatic switchin equipmentin said exchanges, a local source ofoperating current for said subexchange, means for extending talkingconnections from subscribers in one exchange to subscribers in the otherexchange through said switching equipment and over said trunk line, andmeans in said sub-exchange operated responsive to the failure of theoperating current thereat for connecting a particular one of thesub-exchange subscribers to said trunk line independently of theswitching equipment in the subexchange whereby talking connectionsbetween said particular subscriber and subscribers in the main exchangeare established through the main exchange switching equipment and overthe trunk line.

11. In a telephone system, a main and a subexchange, a trunk linebetween said exchanges, subscribers lines terminating in said exchanges,automatic switching equipmentin said exchanges, a local source ofoperating current for said sub-exchange, means for extending talkingconnections from subscribers in one exchange to subscribers in the otherexchange through said switching equipment and over said trunk line,means in said sub-exchange operated responsive to the failure of theoperating current thereat for connecting a particular one of thesub-exchange subscribers to said trunk line independently of theswitching equipment in the sub-exchange whereby talking connectionsbetween said particular subscriber and subscribers in the main exchangeare established through the main exchange switching equipment and overthe trunk line, and means in the sub-exchange controlled over the trunkline during the time that said particular subscriber is using histelephone for preventing the means operated responsive to the failure ofthe sub-exchange operating current from disconnecting said subscriberfrom said trunk line in the event that the sub-exchange operatingcurrent is reestablished.

12. In a telephone system, a main and a subexchange, automatic switchingequipment including a repeater in said exchanges, a trunk line betweensaid exchanges terminating in the repeater at each of said exchanges, asubscriber's line terminating in said main exchange, a subscribers lineterminating in said sub-exchange, a local source of operating currentfor said subexchange, means for extending connections between saidsubscribers through said switching equipment and repeaters and over saidtrunk line, and means responsive to the failure of the said operatingcurrent for extending connections between said subscribers independentlyof said repeaters.

WILLI SCHWENN.

